In case the machine is a bit older, there is no CDROM, nor is a network boot option in the firmware, the only way to proceed is by using good-old floppies. Basically the idea is to get the network to work and copy the files across (see the section called “Network”) - there are several possibilities.
Create a boot and root floppy using the images provided on a T2 server (see the section called “Create a Single Boot/Root Floppy”). Boot and cross your fingers and hope the image provides support for your hardware.
If you use a non-mainstream network card or SCSI setup you may need to build your own floppies. Just add additional kernel options to the bootdisk target's kernel configuration or do other custom modifications to the target. Basically you have to create your own Linux kernel image (see the section called “Linux Kernel”), supporting your hardware, and write it onto the boot CD or floppy.